Revert "Using intervals everywhere"

This reverts commit 9a38b3f809a76fa3f0d05b77b88a7605692d36de.

Conflicts:

	Calendar/src/edu/wpi/cs/wpisuitetng/modules/cal/ui/views/day/DayCalendar.java
	Calendar/src/edu/wpi/cs/wpisuitetng/modules/cal/ui/views/day/collisiondetection/DayItem.java
Fried: Fixing borders